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Understanding water pH in hydroponics

Updated: Mar 13, 2020

pH scale

It’s a hot summer afternoon and you decide to water your plants because they’re wilted. You ask yourself a question, why do they keep dying? pH measures acidity or alkalinity which you must understand in order to grow a healthy plant. If you were gardening on a hot day maybe your water supply isn’t great. That’s another story.


Why is pH important? If the pH of a solution is not within the correct range the plant will not have the ability to absorb some of the essential elements required for proper plant growth. All plants have a particular pH range, which will produce healthy growth, and this level will vary from plant to plant, but most plants prefer a slightly acidic growing environment (5.8 to 6.2). Most plants can survive in an environment with pH values between 5.0 and 7.0.

pH Down

Plants grown in acidic environments can experience a variety of symptoms, including aluminium (Al), hydrogen (H), and/or manganese (Mn) toxicity, as well as nutrient deficiencies of calcium (Ca) and magnesium (Mg).

Conversely, in alkaline environments molybdenum (Mo) and macronutrients (except for phosphorus) availability increases, but phosphorus (P), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu) and cobalt (Co) levels are reduced, and may adversely affect plant growth.

From the chart you can see that each element can become more and less available to the plants as pH changes.  If the pH of your solution is out of the desired range, one or more of the essential elements will become unavailable to the plant, causing nutrient deficiencies, which will result in slow growth rates, and poor yields.

pH Control

Chemical reactions can be inhibited or promoted by the concentration of hydrogen ions in a mixture. We can measure this on a pH scale. Industrial acidic substances are 2.0 pH - lemon, 5.0 pH - coffee, 7.0 pH - milk, 9 pH - baking soda, and 12+ pH - lye. Almost anything that contains hydrogen ions or lack of them can therefore produce a pH. As your plant grows through its life cycle, it adsorbs minerals from the water and deposit waste materials of its own. The removal of nutrients and addition of waste material can cause water pH  levels to fluctuate, so in order to allow for normal course of chemical reactions to take place we need to maintain a desirable pH level. If we don't, we can experience nutrient lockout.

Water pH

Water also has a pH so remember to check your water source. For example: Your medium is 6.0 pH but you want it to be 6.2. You mix a+1 pH and then add it hoping for a 6+1=7. However you forgot that the water you diluted with wasn’t pH measured so you don’t know if you achieved 7 or not until you measure it. Measure your water and your medium to figure out exactly what pH you need. Here’s an example: Water is 5 and medium pH is 4. You would need +2 to make it 7. Then you need +3 for the medium to make it 7. What actually  happens with pH-up and down is somewhat like this but the way you adjust it, by adding a little pH and testing and repeating the procedure, keeping in mind what your water’s pH is. You can always use the pH-up and -down buffering solutions to find pH stability.

pH- Getting back to neutral from acidic

If your soil’s pH in too acidic you will want to bring it back to a neutral 7. You can do this using lime( alkaline calcium oxide), a brittle white caustic solid obtained by heating limestone. You can find lime in containers at your grow shop and add it to your soil the next time you decide to water your plant. Growers know by trial and error how much lime they need to use to push acidic soil back to a pH level of 7. Not all limes work well so be sure to get the gardening lime.

pH- bringing back to neutral from alkaline

If the pH of your soil is too alkaline then you can bring it back to a neutral 7 by adding small amounts of any of the following. Moreover, most growers find a pH-down product more functional.

  • Liquid humic acid

  • Cottonseed meal

  • Lemon peels

  • Coffee Grounds

  • High-acidity fertilizer

These are acidic. Always introduce small amounts of the substance, checking the pH level the next day and readjusting as necessary. Make sure to protect your eyes and skin; you will need to wash them if you come in contact with the pH buffers.


Other pH problems

pH is important because low or high pH levels can cause nutrient lockout. pH irregularities can also cause growth stunting, leaf spots and wilting. Always check the pH level of your soil before treating a nutrient problem. pH is an essential part of growing that you must understand to have harmony with your plants. Thanks for reading.

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